In Alien vs. Predator: Requiem, about 30 minutes into the film, shortly after landing: The Predator who is there to clean up the mess melts the face hugger corpses and the bodies of the hosts of the new Xenomorphs with a blue liquid.

Why does he do this?

Obviously, it's to hide the evidence of the Xenomorphs, but why would the predators want to hide the knowledge of the Xenomorphs from humanity?

In the previous movie (Aliens vs. Predator), they would use their self destruct sequence to prevent the whole planet from being overrun by Xenomorphs, thus losing out on future hunts of the ultimate prey. However, in this case, no more Xenomorphs would pop out of the corpses.